1. Field of the Invention
The present invention relates to a heat radiator assembly for cooling high calorific electronic parts, such as integrated circuits, resistors, and semiconductor elements, mounted on a printed board or the like.
2. Description of the Prior Art
With the recent increase in speed of functioning of semiconductor elements and advancement in the degree of integration, the electric power consumed by a single element has become so large that there are increasing instances where an element becomes highly heated by the heat generated by itself to lower the reliability. According to Arrhenius' principle, the reliability of an element decreases to about half with the increase of about 10 degrees in temperature.
Accordingly, there has been practised forced air cooling with the use of a fan, which, however, has made it necessary to replace the fan periodically because of its life span. For this reason, instead of forced air cooling by a fan, the demand for natural air cooling by natural convection or the like is becoming greater. In such a case where an assembly is installed in a mountainous region where maintenance for replacing the fan is practically impossible, the natural air cooling will be the only way available.
The heat radiation to cool the calorific element is effected by heat transfer from the surface of the heated portion to the surrounding air. Namely, if the resistance of heat transfer between the surface of the heated element and the surrounding air is low, then the heat is well transferred. Therefore, by lowering the heat transfer resistance to the air, better cooling of the heated element is effected. In order to lower the heat transfer resistance to the air, the method to enlarge the surface in contact with the air, i.e. the surface area, has so far been employed.
As a device to achieve the above-stated effect, such one as shown in FIG. 1 has so far been used. In FIG. 1, reference numeral 1 denotes an integrated circuit, IC; the one shown there is of Dual-In-Line package type. Reference numeral 2 denotes a radiating fin, which is made of copper, aluminum, or the like, having good heat conductivity, and the radiating fin is provided with fine grooves 2a on the top face thereof to magnify the surface area in contact with the air. The radiating fin 2 is attached to the top face of the IC 1, a calorific element, with adhesive, as indicated by arrows. The heat generated by the IC 1 is thus conducted to the radiating fin 2 for cooling.
The method to attach the radiating fin 2 directly to the high calorific element IC 1 appears to be effective upon initial consideration, but it involves various problems in reality. Firstly, the direction of the grooves to magnify the surface area of the radiating fin 2 must be in the direction of the air flow. By this arrangement to improve the radiation effect, the direction of the IC 1 to be mounted on the printed board is restricted to be in one direction. As a result, the wiring pattern on the printed board is also subject to restriction.
Secondly, the adhesive used for attaching the radiating fin 2 to IC 1 involves problems. The adhesive must be of the thermal expansion coefficient that conforms to that of the material of the radiating fin 2, e.g. copper, or silver, and that of the package material, e.g. plastic, or ceramic. Besides, the adhesive must endure the thermal stress for a long time, so that the radiating fin 2 is held securely attached to the IC 1. Since such adhesives are expensive and none of them is completely effective at present, in such a construction where the radiating fin 2 is attached to the IC 1 with adhesive, the radiating fin 2 is liable to be separated from the IC 1 when mounted on the printed board subject to vibration or shock, so that such a construction can only be used where there is little or no vibration or shock.
Electronic parts recently used are highly integrated and the elements are manufactured by minute producing technology, and therefore there is an increasing danger that the element may be broken down by electric potential due to static electricity from a human body or the like. For example, C-MOS elements and ordinary MOS elements are the electronic parts that are highly susceptible to be broken down by static electricity. To prevent the electrostatic breakdown of such electronic parts when the same are mounted on a printed board, it is a practice to shield it with a metal case A as shown in FIG. 2. In this case, however, there is a problem that the electronic parts 4 are confined in a narrow space surrounded by the top shield cover 5 and the printed board 3, and therefore the heat emitted from the electronic parts 4 cannot be effectively radiated. Reference numeral 6 denotes a bottom shield cover. Accordingly, the shield case A covers the printed board 3 to prevent the mounted electronic parts 4 from electrostatic breakdown and mechanical damage, but the same has an adverse effect on the electronic parts 4 in the aspect of cooling or heat radiation.
In the conventional heat radiator assemblies as stated above, there have been such disadvantages that the mounting direction of electronic parts has been subject to restriction, or separation of units at the portion where adhesive was applied has been liable to occur, in the case where a radiating fin was attached to electronic parts mounted on a printed board with adhesive, or effective heat radiation from electronic parts to cool the same has been impossible in the case where shielding with a metal case was applied for protection of electronic parts from static electricity.